Sludge-separating centrifuge



June 3, 1969 J sso ET AL 3,447,742

SLUDGE-SEPARAT ING CENTRIFUGE Filed Oct. 21, 1966 Ell-gel- Ensen Arne Nil/sf Y United States Patent US. Cl. 233-7 1 Claim ABSTRACT OF THE DISCLOSURE The centrifugal rotor has an outlet for separated sludge and a separate level-maintaining outlet for separated liquid, the mixture of liquid and sludge being fed into the rotor from the discharge opening of a supply pipe. A screw conveyor has a shaft mounted for rotation in the rotor and is operable to convey centrifugally separated sludge to the sludge outlet; and a circular disc is fixed to this shaft at an axial location between the discharge opening of the supply pipe and the sludge outlet, the disc being coaxial with the screw conveyor and having its periphery lying radially outside the level-maintaining outlet. A second circular disc is fixed to the shaft at an axial location between the discharge opening of the supply pipe and the level-maintaining outlet, the second disc also being coaxial with the screw conveyor and having its periphery lying radially outside the level-maintaining outlet but radially inside the periphery of the first disc.

The present invention relates to sludge-separating centrifuges of the type having a screw conveyor by which centrifugally separated sludge is discharged at one end of the rotor, a level-maintaining outlet at the other end of the rotor for the discharge of separated liquid, a circular disc in the rotor fixed to the shaft of the screw conveyor and coaxial with the screw conveyor, the periphery of this disc lying radially outside the level-maintaining outlet, and a supply pipe extending into the rotor.

When separating a liquid containing fat and water in centrifuges of this kind, it has been found that sludge discharged from the centrifuge has a certain fat content. According to the present invention, this fat content can be avoided by providing a disc similar to that previously mentioned but located axially beyond the opening of the supply pipe, reckoned from the level-maintaining outlet. The disc so located constitutes a barrier for the fat layer, which is formed by the centrifuging as the radially innermost layer, so that the sludge which the screw conveyor removes from the water layer cannot come into contact with the fat. In this way, the sludge discharged from the centrifuge will be free from fat.

The invention is described more in detail below in ref erence to the accompanying drawing, in which the single illustration is a vertical sectional view of an embodiment of the new centrifuge.

In the drawing, a centrifuge rotor 1 has a conical part 13 and is provided at its opposite ends with trunnions 11 and 11a which, by bearings and 10a, are rotatably journalled in a stationary housing 12. Inside the rotor is a screw conveyor 2 arranged to rotate about the same axis as the rotor but driven by shaft 2a at a speed of rotation somewhat different from that of the rotor. The screw conveyor serves to feed centrifugally separated sludge along the conical wall 13 of the rotor to a sludge outlet 14 through which the sludge is discharged under centrifugal force. In the larger end wall 8 of the rotor is an overflow outlet 5. A stationary supply pipe 6 for the material to be treated extends into the rotor. This pipe is coaxial with the rotor and passes through the hollow trunnion 11a. Rotor 1 is driven in any suitable manner, as through gearing (not shown) connected to trunnion 11.

When a centrifuge of the type initially described is in operation, the material fed from supply pipe 6 forms an annulus 15 at the inside of the rotor, due to the action of centrifugal force. The centrifugal force divides this annulus into annular layers, due to the different specific gravities of the components of the feed mixture. For example, if a mixture of water, oil and sludge is to be separated, the mixture is divided centrifugally into an oil layer located nearest the rotation axis, then a water layer, and then a sludge layer located farthest from the rotor axis. As screw conveyor 2 feeds the sludge along the inside of the rotor wall towards its outlet 14, the sludge will thus pass through the oil layer lying nearest the rotor axis and contacting the conical wall 13 of the rotor. It is obvious that the sludge will then entrain a substantial quantity of oil, which is lost.

According to the present invention, a circular disc 4 is fixed to the shaft 3 of the screw conveyor 2 and is coaxial with the screw conveyor, the periphery of this disc lying radially outside the overflow outlet 5. Disc 4 is located axially beyond the opening 7 of the supply pipe 6, reckoned from the outlet 5, and forms a dam which prevents the separated oil layer from flowing in the direction toward the sludge outlet 14. Consequently, when the sludge phase is fed radially inward through the liquid phase by the screw conveyor, the sludge will not pass through any oil layer but only through a water layer. The sludge will thus be completely free from oil. The location where the circular disc 4 is fixed to the screw conveyor shaft 3 will be seen from the drawing.

It may happen that solid fat lumps are contained in the material which is fed to the centrifuge through the supply pipe 6. These fat lumps often contain substantial quantities of sludge particles. Normally, these lumps will float on the annular liquid surface and discharge through the outlet 5, whereby the separated fat phase will contain contaminating sludge. In order to prevent this, a circular disc 4a is fixed to the screw conveyor shaft 3 at an axial location between the opening 7 of the supply pipe 6 and the level-maintaining outlet 5. The periphery of the disc 4a lies radially outside the level-maintaining outlet 5 and prevents the floating fat lumps from reaching that outlet. After some time they melt, whereupon the released sludge is centrifugally separated and joins the sludge conveyed to the sludge outlet 14. Obviously, the diameter of the discs is chosen so that the disc 4 extends radially through at least the whole thickness of the oil layer, whereas the disc 4a mainly breaks only the surface of the oil layer.

We claim:

1. In a sludge-separating centrifuge, the combination of a centrifugal rotor, a supply pipe extending into the rotor and having an opening for discharging a mixture of liquid and sludge into the rotor, the rotor having an outlet for centrifugally separated sludge and a separate level-maintaining outlet for centrifugally separated liquid, a screw conveyor in the rotor operable to convey centrifugally separated sludge to said sludge outlet, said conveyor having a shaft mounted for rotation in the rotor, a circular disc fixed to said shaft at an axial location between said discharge opening of the supply pipe and said sludge outlet, said disc being coaxial with the rotation axis of the screw conveyor and having its periphery lying radially outside said level-maintaining outlet, and a second circular disc fixed to said shaft at an axial location between said discharge opening of the supply pipe and said level-maintaining outlet, the second disc also being coaxial with the rotation axis of the screw conveyor and having its periphery lying radially outside said 4 level-maintain ing outlet but radially inside said periphery FOREIGN PATENTS 0f the 1,753,992 10/1957 Germany.

References 364,348 1/1932 Great Britain.

UNITED STATES PATENTS 3,228,594 1/1966 Amero 2337 0 r HENRY T. KLINKSIEK, Primary Examiner. 

